Java-Three Layer Architecture Design

• Abstraction
  • eliminate irrelevant details
  • ignore relevant detail which is not need for current task
  • generalize problem
    • reusable
    • handle more situations
• Decomposition
  • divide larger task to small sub=parts
  • solve each sub-task with a module or more
  • combine those modules
  • each module need a specification of what sub-task do
    • develop when dividing
    • reason why module like this
    • final specification for combine
    • final specification used when solve problem
  • specification contain
    • signature
    • precondition
    • postcondition
    • return value
  • Guideline of Decomposition
    • Locality
      • keep related thing inside one class
    • Strong cohesion
      • everything inside one module should focus on same purpose
    • Weak coupling
      • minimize interaction between modules
      • if so, merge them or parts of them
      • each entities only know certain about others
      • how entities does job is hidden from other parts of system
      • each entities have own abstract specification
• Sequence of Instructions fro Interactive System
  • read specification for what operation to do
  • determine what command do
  • if necessary, read in the data for the command
  • execute command
    • may be many part to do
      • exp. calc, get info from file….
    • separate it
      • I/O to interface
      • calc as a command and get-info as a command….
      • each command as a separate class(use command as object, called Command Pattern)
        • easy to add/remove command
        • do/redo/undo a command
        • can save command for later execution
        • send a command to where executed
  • output result
• Class Classification
  • 1. entity class
    • basic data structure and methods
  • 2.container class
    • container of entities
  • 3. control class
    • main program and test
  • 4. interface class
    • control I/O
    • handle communication between system and entities
• Three Layers
  • Presentation Layer
    • user Interface
      • Handle I/O
    • startup
      • Internalize System
        • active container
    • controller
      • determine next operation
      • obtain parameter
      • execute operation
      • handle result of operation
  • Domain Layer
    • commands
      • actual operation
      • handle error input/output
        • invoke a mutator for error message, store in a field of command
        • output it if error happened
        • check commandStatus class in assignment
    • container
      • data storage of entities
  • System Layer
    • entities
      • actual data structure and their own methods